A card-type electronic apparatus containing a memory device (e.g., an electrically erasable programmable read-only memory (EEPROM) or “flash” memory chip) and other semiconductor components is referred to as a memory card. Typical memory cards include a printed circuit board assembly (PCBA) mounted or molded inside a protective housing or casing. The PCBA typically includes a printed circuit substrate (referred to herein simply as a “substrate”) formed using known printed circuit board fabrication techniques, with the memory device and additional components (e.g., control circuitry, resistors, capacitors, etc.) formed on an upper surface of the substrate (i.e., inside the casing), and one or more rows of contact pads exposed on a lower surface of the substrate. The contact pads are typically aligned in a width direction of the casing, and serve to electrically connect and transmit electrical signals between the memory chip/control circuitry and a card-hosting device (e.g., a computer circuit board or a digital camera). Examples of such portable memory cards include multi media cards (MMC cards), personal computer memory card international association (PCMCIA) cards. An exemplary MMC card form factor is 24 mm wide, 32 mm long, and 1.4 mm or 1.5 mm thick, and is substantially rectangular except for a chamfer formed in one corner, which defines the front end of the card that is inserted into a card-hosting device. The card's contact pads are exposed on its lower surface of each card near the front end. These and other similar card-like structures are collectively referred to herein as “memory module cards” or simply as “memory cards”.
An important aspect of most memory card structures is that they meet size specifications for a given memory card type. In particular, the size of the casing or housing, and more particularly the width and thickness (height) of the casing/housing, must be precisely formed so that the memory card can be received within a corresponding slot (or other docking structure) formed on an associated card-hosting device. For example, using the MMC card specifications mentioned above, each MMC card must meet the specified 24 mm width and 1.4/1.5 mm thickness specifications in order to be usable in devices that support this MMC card type. That is, if the width/thickness specifications of a memory card are too small or too large, then the card can either fail to make the necessary contact pad-to-card-hosting device connections, or fail to fit within the corresponding slot of the associated card-hosting device.
One conventional method for manufacturing memory cards that meet required size specifications includes using a cover or housing that is typically adhesively attached to the PCBA substrate over the semiconductor components. One shortcoming of this approach is that the thickness of such covers is necessarily relatively thick, and therefore takes up a significant amount of the specified memory card thickness (e.g., the 1.4 mm thickness of standard MMC cards). As a result, the choice of memory device and other components mounted used in these memory cards is limited to devices that are relatively thin. In addition, because such covers are fabricated separately and then attached to the substrate using an adhesive, the use of such separate covers increases production and assembly costs, and the covers can become detached from the substrate.
U.S. Pat. No. 6,462,273 discloses a second conventional MMC card fabrication process that avoids the thickness problems associated with separate cover structures by forming a molded casing over the PCBA components. First, the PCBA is assembled using normal practices by forming individual module substrates that are connected to a common carrier, with the material used for the carrier being the same as that of the module substrate. During a subsequent plastic molding process, round shaped rods are utilized for forming notches on the card body. Later, round shape cutters are cutting through the notched areas. If any connecting portion between the module and the carrier is not being cut clean, such that there are remaining silvers attached to the module, the silvers will not exist beyond the notch area and affect the card size specifications. Therefore, the card manufactured by this method has notches on the card body.
A problem with the manufacturing method disclosed in U.S. Pat. No. 6,462,273 is that the resulting memory card includes notches that reduce the usable area of the substrate in the width direction. In addition, portions of the substrate remain exposed in the notches after the carrier separation process, which further limits the use of the substrate in regions adjacent to the notches due to possible contamination and/or damage to the substrate in these regions.
What is needed is a method for producing memory cards that utilizes low-cost molding techniques to form rigid casing over a PCBA that maximizes the usable substrate area and avoids the contamination problems associated with conventional molding techniques.